Thermal transfer processes are well known in applications such as color proofing as a means of dry transferring or printing of dye and/or pigment layers. Such thermal transfer processes typically use a laser to induce the image-wise thermal transfer of material.
Laser-induced thermal transfer processes typically use a donor element, including a layer of material to be transferred, referred to herein as a transfer layer, and a receiver element, including a surface for receiving the transferred material. Either the substrate of the donor element or the receiver element is transparent, or both are transparent. The donor element and receiver element are brought into close proximity or into contact with each other and selectively exposed to laser radiation, usually by an infrared laser. Heat is generated in the exposed portions of the transfer layer, causing the transfer of those portions of the transfer layer onto the surface of the receiver element. If the material of the transfer layer does not absorb the incoming laser radiation, the donor element should include a heating layer, also known as a light-to-heat conversion (LTHC) layer or a transfer-assist layer, in addition to the transfer layer.
In a typical laser-induced digital thermal transfer process the exposure takes place only in a small, selected region of the assembly at a time, so that transfer of material from the donor element to the receiver element can be built up one region at a time. The region may be a pixel, some portion of a pixel or a plurality of pixels. Computer control facilitates the transfer at high speed and high resolution. Alternatively, in an analog process, the entire assembly is irradiated and a mask is used to selectively expose desired portions of the thermally imageable layer, see for instance, U.S. Pat. No. 5,937,272.
A particular need for printable electronics includes thermally imageable insulating layers; conducting metal layers; conducting polymer layers; color layers; semiconductor layers and light emitting layers, among others. Thermal printing of these various layers requires very efficient and clean transfer processes in order to ultimately provide a functioning electrical device of sufficient quality. In some instances, depending upon the nature of the donor and receiver elements and the transfer processing parameters, when the donor element and the receiver element are separated after thermal transfer, the receiver element includes both exposed portions and some non-exposed portions of one or more transfer layers. A process is needed to enhance the resolution of the thermally transferred pattern on a thermal transfer receiver by removal of the non-exposed portions of various transferred transfer layers, preferably using a dry process; that is, without the use of solvents.